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Focusing on Energy to compare BEVs and ICEVs


Photo by Vlad Tchompalov on Unsplash
Photo by Robert Haverly on Unsplash

tldr: Total energy consumption, throughout a 200k mile life of a car, is estimated to be 74 MWh for a battery electric vehicle (BEV), and 245 MWh for an internal combustion engine vehicle (ICEV). BEVs requires almost 3 times more energy to produce than an ICEV, but are about 5 times more efficient during the use phase. EPA economy estimates for a Model 3 SR+, and the EPA real-world economy average for a Sedan/Wagon, were used as inputs for the use phase energy consumption of a BEV and ICEV, respectively. The production phase energy consumption estimate for a BEV was extrapolated from an emissions figure found in the 2019 Tesla Impact Report, while the production phase energy consumption estimate for an ICEV was found in the detailed study by Sullivan, 2010. Details on this analysis are below.

Total energy consumption of a BEV and ICEV throughout a 200k mile life. Absolute consumption for use phase and production phase is shown. Units are in MWh (megawatt-hours) = 1000 kWh (kilowatt-hours).


Reducing consumption is a fool-proof solution to the issue of climate change and depletion of Earth's resources.


Focusing on energy

Most comparisons between electric cars and conventional gasoline powered cars are based on greenhouse gas emissions (carbon dioxide). I believe strictly comparing relative greenhouse gas emissions between alternatives in the transportation sector, clouds our vision of sustainable behavior. By focusing on greenhouse gas emissions, only, and putting blinders up to other externalities, we have opened up an endless list of justifications for more consumption. Further complicating the matter for electric vehicles, is that the electricity in the grid used to charge those vehicles comes from a variety of sources, and the variety even varies across the country. This leads to misleading conclusions that an electric car in one part of the country is not as effective at combating climate change as it might be in another. What practical decisions can an end consumer make with information like this?

Source: U.S. Energy Information Administration, Monthly Energy Review, March 2020


Another exemplary repercussion of the strictly-greenhouse-gas-emission approach, is that 11 of the 14 major automotive manufactures had to purchase greenhouse gas credits through the EPA’s ABT program to maintain compliance with the EPA's already mediocre, and politically loaded SAFE targets. To me, this is a breakdown of the regulatory agency's primary mission, and allows automotive manufactures to buy their way out of overly-polluting fleets.

CO2 Performance and Standards by Manufacturer, Model Year 2019. Source: epa.gov


The Simple Solution

If we could instead simply look at the overall energy consumption of various alternatives, we would make far better decisions as the end consumer. Reducing consumption is a fool-proof solution to the issue of climate change and depletion of Earth's resources.


From the perspective of the consumer

This analysis is from the perspective of the consumer, not the manufacturer, which differs from most reports I have seen. Energy consumed throughout the entire life of the car is important to the manufacturer, but what really matters is the demand. How much energy is consumed by the end consumer is the behavior we must analyze, and improve.

Again, by focusing on the supply side (manufacturer and vehicle), we are dehumanizing the problem. EPA standards and advancements in technology are not standalone solutions, but help facilitate the demand-side change necessary to curb unsustainable consumption.

EPA standards and advancements in technology are not standalone solutions, but help facilitate the demand-side change necessary to curb unsustainable consumption.

My motivation

I had a few questions regarding my next car purchase, which motivated me to do this simple analysis. Included here are the answers, for which details on the calculations are further below.

  1. At what point in the life of a BEV, measured in miles driven, will the overall energy consumed become less than that of an ICEV (factoring both production and use phase consumption)? 18,070 miles

  2. If I buy a used ICEV instead of a new BEV with the intention of reducing energy consumption, how many miles should I drive it? less than 28,111 miles

  3. Over the entire life of a BEV and ICEV, how much total energy will each consume? BEV = 74 MWh = 74,000 kWh ICEV = 245 MWh = 245,000 kWh

To help us calibrate exactly how much a kWh is, Electricity Plans published a handy cheat sheet:

  • an average US home consumes 877 kWh per month

  • an electric water heater consumes 380-500 kWh per month

  • an electric car uses about 1 kWh to drive 4 miles

  • and, the EIA shows us that all US electricity retail sales amounted to almost 4 trillion kWh in 2019 (basically, all the electricity consumed in the US annually)

Energy storage in a car

How is energy stored in an internal combustion engine vehicle (ICEV)?

Gasoline, a refined fossil fuel product, stores energy for use in driving an ICEV. Even a small, 10 gallon gas tank, holds 364 kWh of energy.

So, how do we store energy in an electric vehicle?

The main contender for passenger cars, today, is a lithium-ion battery pack. Hence the name battery electric vehicle, or BEV. Even the best and largest battery packs don't come close to having the energy capacity of a small gas tank. For example, the Model S Long Range Plus has a battery pack capacity of 100kWh, according to Car and Driver. This is less than a third of a small gas tank. BEVs make up for this by being much more efficient while driving than ICEVs.

How much more efficient are BEVs than ICEVs?

During the use phase, when the car is actually driven, BEVs are way more efficient than ICEVs because of how an electric motor works, compared to an internal combustion engine. The complication is that it takes much more energy to produce a BEV than an ICEV. ICEVs come with an empty gas tank, while a BEV comes with a heavy battery pack full of expensive elements (lithium, nickel, cobalt, etc). Also, ICEVs are manufactured at larger scales, with mature manufacturing practices, such that they are produced more efficiently relative to the "immature" BEVs.


The battery in the Model 3 is the large rectangular block that sits underneath the cabin. (2017_Model_3_Emergency_Response_Guide-high-voltage)


Analysis

The analysis compares the production and use phase energy consumption for a Model 3 SR+, and an average sedan passenger car in the US.


Use Phase

For the use phase estimate, the EPA economy rating for the 2020 Model 3 SR+, and the 2019 EPA real-world economy estimate for a sedan/wagon, are used. The economy estimate for the average ICEV (in mpg) is slightly generous because electric vehicles are actually increasing the average economy for sedans/wagons, but it is still representative of the modern ICEV sedan for the purposes of this analysis because electric vehicles only make up ~2% of the fleet (EEI).


To convert the mpg estimate for an ICEV to [Watt*hours/mile], the energy density of gasoline is used. In these units, it is clear that ICEVs are much more inefficient than BEVs during the use phase (when the car is driven). An average ICEV sedan will consume about 5 times more energy per mile driven than a BEV.




Production Phase

It was difficult to get an accurate estimate for the energy requirement to produce a Tesla Model 3. An attempt is made here to extrapolate the production energy requirement, from the CO2 emission estimate published in the 2019 Tesla Impact Report. With the expected life of the vehicle in miles, and the CO2 emissions for electricity in the grid is estimated in [gCO2/(kW*h)], the total energy consumed for production can be roughly deduced (as shown below).




The energy requirement for the production phase of an average ICEV was found in a detailed and meticulous report published by Sullivan, 2010. BEVs require almost 3 times as much energy to produce than ICEVs, according to this estimate. This is due to the production of the battery pack in a BEV, and because ICEVs are produced at much larger scales (millions instead of hundreds of thousands).



Total Energy

Combining the use and production phases, we can estimate the total energy consumed by driving a BEV and an ICEV. At zero miles, when the consumer buys a new car, the energy consumed comes only from the production phase. As they drive, the energy consumes increases. Although the BEV production energy requirement is higher than the ICEV, there is a crossing point where the BEV becomes more efficient overall because the BEV consumes much less energy during the use phase.




Over the life of the car, the much more efficient-driving BEV will consume about 3.3 times less energy than an ICEV, despite the fact that it takes about 2.8 times more energy to produce. It is also important to note that the majority of the energy consumed, in absolute, by both BEVs and ICEVs is during the use phase (when the car is driven).



Finally, if the consumer were to buy a used ICEV instead of a BEV, with the intention of saving energy, they should drive it less than 28,111 miles. This way, energy will be saved by not producing that BEV, and instead taking advantage of the plentiful used ICEV market. If that used ICEV is driven more than 28,111 miles, then it would have been more efficient to buy a new BEV in the first place.




Details on the calculations

Here is the MathCAD file I created to calculate the energy analysis described above.


MathCAD Calculations Doc - PDF

MathCAD Calculations Doc - mcdx



References

2020 Tesla Model S Features And Specs. Car and Driver.

https://www.caranddriver.com/tesla/model-s/specs

Electric Vehicle Sales: Facts & Figures. (2019, April). Edison Electric Institute (EEI). https://www.eei.org/issuesandpolicy/electrictransportation/Documents/FINAL_EV_Sales_Update_April2019.pdf

Electricity explained, Electricity in the United States. (2020, August 28). U.S. Energy Information Administration (EIA).

https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php

Electricity explained, Use of Electricity. (2020, August 28). U.S. Energy Information Administration (EIA).

https://www.eia.gov/energyexplained/electricity/use-of-electricity.php

Highlights of the Automotive Trends Report. (2021, January). Environmental Protection Agency (EPA).

https://www.epa.gov/automotive-trends/highlights-automotive-trends-report

How much carbon dioxide is produced per kilowatthour of U.S. electricity generation? (2020, December 15). U.S. Energy Information Administration (EIA).

https://www.eia.gov/tools/faqs/faq.php?id=74&t=11

How much electricity does an American home use? (2020, October 9). U.S. Energy Information Administration (EIA).

https://www.eia.gov/tools/faqs/faq.php?id=97&t=3

Impact Report 2019. (2019). Tesla.

https://www.tesla.com/ns_videos/2019-tesla-impact-report.pdf

SAFE. (2020, July 09). National Highway Traffic Safety Administration (NHTSA).

https://www.nhtsa.gov/corporate-average-fuel-economy/safe

Sullivan, J L, Burnham, A, Wang, M, & Energy Systems. Energy-consumption and carbon-emission analysis of vehicle and component manufacturing.. United States. https://doi.org/10.2172/993394

Tesla Model 3 Standard Range Plus. (2020). US Department of Energy (DoE). https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=42278

What Is A Kilowatt-hour (kWh) And What Can It Power? (2020, December 16). Electricity Plans.

https://electricityplans.com/kwh-kilowatt-hour-can-power/

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